Please please explain this immediatelyy.

Dear student
Isoelectronic species are t​hose species which have same number of electrons.
So O2-, Mg2+ and Al3+ all have 10 electrons each.
We know that an anion is bigger in size than an atom and a cation as well.Moreover the nuclear charge on the species is inversely proportional to the atomic size. So O2- is the largest of all species present and Al3+ is the smallest.
O2- > Ne> ​ Mg2+ > ​Al3+